1 European journal of human genetics : EJHG 2006 Vol: 14(12):1288-1294. DOI: 10.1038/sj.ejhg.5201709

The scale and nature of Viking settlement in Ireland from Y-chromosome admixture analysis.

The Vikings (or Norse) played a prominent role in Irish history but, despite this, their genetic legacy in Ireland, which may provide insights into the nature and scale of their immigration, is largely unexplored. Irish surnames, some of which are thought to have Norse roots, are paternally inherited in a similar manner to Y-chromosomes. The correspondence of Scandinavian patrilineal ancestry in a cohort of Irish men bearing surnames of putative Norse origin was examined using both slow mutating unique event polymorphisms and relatively rapidly changing short tandem repeat Y-chromosome markers. Irish and Scandinavian admixture proportions were explored for both systems using six different admixture estimators, allowing a parallel investigation of the impact of method and marker type in Y-chromosome admixture analysis. Admixture proportion estimates in the putative Norse surname group were highly consistent and detected little trace of Scandinavian ancestry. In addition, there is scant evidence of Scandinavian Y-chromosome introgression in a general Irish population sample. Although conclusions are largely dependent on the accurate identification of Norse surnames, the findings are consistent with a relatively small number of Norse settlers (and descendents) migrating to Ireland during the Viking period (ca. AD 800-1200) suggesting that Norse colonial settlements might have been largely composed of indigenous Irish. This observation adds to previous genetic studies that point to a flexible Viking settlement approach across North Atlantic Europe.

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Figures
FIGURE 1


Y-chromosome haplogroup/haplotype frequencies in the Irish NSG and Irish and Norwegian potential parental populations. The modal STR profiles for specific lineages are (DYS19, DYS388, DYS390, DYS391, DYS392, DYS393): AMH (14, 12, 24, 11, 13, 13); 2.47 (14, 14, 22, 10, 11, 13); 3.65 (16, 12, 25, 11, 11, 13). '+1' refers to one-step (STR repeat unit) mutational neighbours. FIGURE 2


Inter-relationship of the NSG and other North-Atlantic European populations. The graphs plot dimension 1 versus dimension 2 of the variation in pairwise genetic distance matrices based on (a) UEP and (b) STR Y-chromosome markers. There is a clear separation in both cases, of the Irish and Norwegian parental populations. The closer affinity of the NSG to Ireland is also readily apparent, especially in STR variation. The S-stress and RSQ values for the MDS analysis in plot (a) are 0.038 and 0.995, respectively, whereas those for plot (b) are 0.039 and 0.994, respectively. FIGURE 3


Irish (P1) admixture proportion estimates for the NSG. Analysis was carried out using six different estimators (m R , m C , m Y , m L, m W, m ) independently for UEP and STR Y-chromosome diversity (m was developed for STR variation and was therefore not estimated for UEP haplogroups). Associated confidence boundaries for each estimator are also shown (with the exception of m C as the LEADMIX software does not return a confidence interval for single-locus estimates). m R, m C and m Y are unconstrained estimators and may return notional admixture proportions greater than 1. FIGURE 4


MCMC convergence of the m L admixture estimator. Each line shows the posterior probability density function of Irish (P1) ancestry, over 50 000 iterations, based on UEP Y-chromosome variation (11 alleles) or six locus STR haplotypes (106 alleles). Whereas the UEP run showed little convergence, that based on STR variation showed an unambiguous tendency toward a high Irish ancestry proportion estimate.
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References
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    • . . . After first recorded contact in AD 795 they are credited with establishing Ireland's first true urban settlements including modern Dublin, Limerick and Cork.1, 2 It is generally agreed that present day Norway was the source of Ireland's Viking raiders and settlers but despite their apparent historical prominence, other lines of evidence, including the scarcity of Norse place names in Ireland and the paucity of word borrowing from Norse into Irish, argue against any large-scale Viking immigration.3 In addition, there also appears to have been extensive integration between the Irish and Norse leading to a fusion 'Hiberno–Norse' material culture in areas of Viking settlement . . .
    • . . . Unlike many areas of the British Isles, Norse kingdoms in Ireland were limited in contiguous geographic extent1 and centred on now highly urbanised cities making it difficult to reliably identify modern potential Norse-Irish geographic populations . . .
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    • . . . After first recorded contact in AD 795 they are credited with establishing Ireland's first true urban settlements including modern Dublin, Limerick and Cork.1, 2 It is generally agreed that present day Norway was the source of Ireland's Viking raiders and settlers but despite their apparent historical prominence, other lines of evidence, including the scarcity of Norse place names in Ireland and the paucity of word borrowing from Norse into Irish, argue against any large-scale Viking immigration.3 In addition, there also appears to have been extensive integration between the Irish and Norse leading to a fusion 'Hiberno–Norse' material culture in areas of Viking settlement . . .
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    • . . . After first recorded contact in AD 795 they are credited with establishing Ireland's first true urban settlements including modern Dublin, Limerick and Cork.1, 2 It is generally agreed that present day Norway was the source of Ireland's Viking raiders and settlers but despite their apparent historical prominence, other lines of evidence, including the scarcity of Norse place names in Ireland and the paucity of word borrowing from Norse into Irish, argue against any large-scale Viking immigration.3 In addition, there also appears to have been extensive integration between the Irish and Norse leading to a fusion 'Hiberno–Norse' material culture in areas of Viking settlement . . .
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    • . . . The genetic legacy of the Viking age is well characterised for many areas of North Atlantic Europe.5, 6, 7, 8 However, there has been relatively little investigation of their impact on the Irish gene pool . . .
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    • . . . The genetic legacy of the Viking age is well characterised for many areas of North Atlantic Europe.5, 6, 7, 8 However, there has been relatively little investigation of their impact on the Irish gene pool . . .
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    • . . . The genetic legacy of the Viking age is well characterised for many areas of North Atlantic Europe.5, 6, 7, 8 However, there has been relatively little investigation of their impact on the Irish gene pool . . .
    • . . . These included roughly equal male and female contributions through family-based migration, to secure settlements near Scandinavia and the integration of Gaelic females on frontier settlements further west, predominantly founded by Norse males.8 In Ireland successful settlement may have involved the wholesale incorporation of the indigenous Irish to create a distinctive, fusion Hiberno–Norse colonial society. . . .
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    • . . . Principal component analysis (PCA) of Y-chromosome allele (haplogroup) frequencies suggested little or no Norse introgression in Ireland, whereas maximum likelihood admixture calculations indicated a substantial 34.8% Norwegian ancestry in a Dublin hinterland sample.9 However, the confidence intervals on this estimate encompassed virtually zero to total Norwegian ancestry. . . .
    • . . . The current data were analysed primarily in concert with published Y-chromosome data for Ireland, Scandinavia and Britain.9 Norse surname group (NSG) Y-chromosomes were divided into haplogroups as outlined by Capelli et al.9 The single nucleotide polymorphisms M173 and M17 used in the former study were not typed in the NSG . . .
    • . . . UEP alleles are simply represented by the 11 haplogroups defined in Capelli et al9 whereas Y-chromosome STR alleles are compound haplotypes of six STR loci . . .
    • . . . The first parental population (P1) was an Irish sample (n=119), whereas a Norwegian sample (n=201) represented the second parental population (P2).9 This data set was chosen to allow strict comparability in sample populations between UEP and STR-based admixtures estimates . . .
    • . . . Norwegian (n=201) and Danish/North German (n=190) population samples were taken directly from Capelli et al9 while a number of British Isles subpopulations were generated from the same data by combining smaller groupings as follows (n): Ireland (119); Scottish Isles (272); Scotland (178); Wales (196); England North (231); England Midlands (205); England Southwest (125); England Southeast (256). . . .
    • . . . The N3 and P R1 haplogroups also found in Norway at appreciable frequencies are absent in the British Isles (other than the Orkney Islands)9 and the NSG . . .
    • . . . For example, there are multiple instances of the E3b haplogroup that is more typical of England than either Ireland or Scandinavia.9 Alternatively, unique haplotypes, might indicate the action of drift over time . . .
    • . . . This observation may explain, in part at least, previous mL Y-chromosome admixture estimates indicating high (35%) Scandinavian ancestry in a Dublin hinterland sample.9 It may also be a relevant consideration in resolving the widely discrepant estimates of modern European ancestry attributed to the Neolithic or Palaeolithic periods using the same Y-chromosome data but different approaches, including mL.35, 36 . . .
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    • . . . As an alternative approach, we used the patrilineal coinheritance of surnames and Y-chromosomes.10 Surnames were first adopted in Ireland from ca . . .
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    • . . . A previous Irish Y-chromosome11 study using this approach successfully identified a distinctive paternal population history for Irish groups with surnames of exogenous (English and Scottish) origin . . .
    • . . . We also conducted additional admixture analysis with these methods using independent parental populations data sets including a larger Irish grouping (n=221)11 and separate Norwegian (n=250),6, 30, 31 Danish (n=69)6, 32 or Swedish (n=110)30 populations . . .
    • . . . Although the use of surname information to investigate historical questions is potentially powerful11, 16, 17 any inference inherently relies on the accurate assessment of surname origin . . .
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    • . . . Norse surnames were identified according to McLysaght,12 the major general reference for individual Irish surname origins . . .
    • . . . The perturbed nature of Irish surname history means that similar or identical names can have more than one source.12, 17, 33 For example, the name Sweetman can be of Norse origin or English toponymic from Swettenham.12 The presence of several haplotypes within the NSG not found in the Irish or Norwegian samples may hint at this possibility . . .
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    • . . . DNA was extracted using a standard phenol/chloroform protocol and each sample genotyped for 13 STR loci (DYS19, DYS388, DYS390, DYS391, DYS392, DYS393, DYS385A, DYS385B, DYS389I, DYS389II, DYS460, DYS461, and DYS462) in two multiplexes (MS1 and EBF) essentially as previously described.13 Up to six UEPs (M269, M170, M26, SRY-1532.2 (SRY10831.2), M35, YAP), which divide samples into broader haplogroups,14, 15 were also examined in a hierarchical manner using polymerase chain reaction/restriction fragment length polymorphism assays . . .
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    • . . . DNA was extracted using a standard phenol/chloroform protocol and each sample genotyped for 13 STR loci (DYS19, DYS388, DYS390, DYS391, DYS392, DYS393, DYS385A, DYS385B, DYS389I, DYS389II, DYS460, DYS461, and DYS462) in two multiplexes (MS1 and EBF) essentially as previously described.13 Up to six UEPs (M269, M170, M26, SRY-1532.2 (SRY10831.2), M35, YAP), which divide samples into broader haplogroups,14, 15 were also examined in a hierarchical manner using polymerase chain reaction/restriction fragment length polymorphism assays . . .
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    • . . . DNA was extracted using a standard phenol/chloroform protocol and each sample genotyped for 13 STR loci (DYS19, DYS388, DYS390, DYS391, DYS392, DYS393, DYS385A, DYS385B, DYS389I, DYS389II, DYS460, DYS461, and DYS462) in two multiplexes (MS1 and EBF) essentially as previously described.13 Up to six UEPs (M269, M170, M26, SRY-1532.2 (SRY10831.2), M35, YAP), which divide samples into broader haplogroups,14, 15 were also examined in a hierarchical manner using polymerase chain reaction/restriction fragment length polymorphism assays . . .
    • . . . Virtually all North-West Europe haplogroup R Y-chromosomes appear to either have the derived allele for SRY1532.2 and M17 or M173 and M269 meaning that this treatment introduces minimal error (the full Y-chromosome phylogenetic tree can be seen in Jobling and Tyler-Smith15) . . .
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    • . . . The haplogroups of the remaining four samples were inferred from their STR profiles by comparison to a database of 2000 Irish Y-chromosomes16, 17 typed for these STRs and UEPs. . . .
    • . . . We also examined the occurrence of these putative Viking marker lineages in a general Irish population sample of 796 Y-chromosomes.16 However, these are not frequent (<0.5%) in the Irish population as a whole nor do they comprise a large fraction of Y-chromosomes in any of nine smaller geographic Irish subgroupings, indicating no strong regional-specific introgression. . . .
    • . . . Although the use of surname information to investigate historical questions is potentially powerful11, 16, 17 any inference inherently relies on the accurate assessment of surname origin . . .
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    • . . . The haplogroups of the remaining four samples were inferred from their STR profiles by comparison to a database of 2000 Irish Y-chromosomes16, 17 typed for these STRs and UEPs. . . .
    • . . . There is a generally strong correlation of Irish surnames with Y-chromosomes indicating shared recent patrilineal ancestry.17 However, this varies considerably between names, reflecting different origins (single versus multiple founders) and the impact of post-foundation male introgression . . .
    • . . . Although the use of surname information to investigate historical questions is potentially powerful11, 16, 17 any inference inherently relies on the accurate assessment of surname origin . . .
    • . . . We have previously estimated this rate at 1.6% per generation,17 which would be expected to roughly halve any initial Scandinavian ancestry fraction over 1000 years (40 generations) . . .
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    • . . . Several different admixture estimation methodologies are commonly used, many of which try to incorporate some of these potential complications.18 However, no current admixture method can fully account for all of them . . .
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    • . . . Once again analysis was conducted independently for UEP and STR markers using the ARLEQUIN package28 (Version 2.000) . . .
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    • . . . Two such UEP/STR-defined haplotypes and their one-step STR neighbours ('+1' those haplotypes differing by one STR repeat over all loci) are found at high frequency in Norway (representing the Viking source population) and other areas affected by Viking migrations.29 These types, termed 2.47+1 and 3.65+1, are either absent or at low frequency in the NSG (Figure 1) . . .
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    • . . . We also conducted additional admixture analysis with these methods using independent parental populations data sets including a larger Irish grouping (n=221)11 and separate Norwegian (n=250),6, 30, 31 Danish (n=69)6, 32 or Swedish (n=110)30 populations . . .
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    • . . . We also conducted additional admixture analysis with these methods using independent parental populations data sets including a larger Irish grouping (n=221)11 and separate Norwegian (n=250),6, 30, 31 Danish (n=69)6, 32 or Swedish (n=110)30 populations . . .
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    • . . . We also conducted additional admixture analysis with these methods using independent parental populations data sets including a larger Irish grouping (n=221)11 and separate Norwegian (n=250),6, 30, 31 Danish (n=69)6, 32 or Swedish (n=110)30 populations . . .
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    • . . . The perturbed nature of Irish surname history means that similar or identical names can have more than one source.12, 17, 33 For example, the name Sweetman can be of Norse origin or English toponymic from Swettenham.12 The presence of several haplotypes within the NSG not found in the Irish or Norwegian samples may hint at this possibility . . .
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    • . . . There is some evidence that they had a degree of popularity in a native Irish context34 and if such exchange was common it may mean that Norse names had begun to become disassociated with Norse colonial societies by the time of widespread surname adoption . . .
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